public class ListNodePartition {

    public class ListNode {
        int val;
        ListNode next = null;

        ListNode(int val) {
            this.val = val;
        }
    }
    public ListNode partition(ListNode head, int x) {
        if (head == null || head.next == null) {
            return head;
        }
        ListNode cur = head;
        ListNode bs = null;
        ListNode be = null;
        ListNode as = null;
        ListNode ae = null;

        while (cur != null) {
            if (cur.val < x) {
                if (bs == null) {
                    bs = cur;
                    be = cur;
                } else {
                    be.next = cur;
                    be = be.next;
                }
            } else {
                if (as == null) {
                    as = cur;
                    ae = cur;
                }else {
                    ae.next = cur;
                    ae = ae.next;
                }
            }
            cur = cur.next;
        }

        if (bs == null) {
            return as;
        }

        be.next = as;

        if (as != null) {
            ae.next = null;
        }
        return bs;
    }
}
